Signors to the s



June 2, 1931. T. A. SWARTZ ET AL VARIABLE RESISTANCE UNIT Filed Jan. 27,1925 FIG: 2.. FIG 51 anon H 01;

FIG: 7. J6 AH 55 6965 1 WW cum 3 a y: a; 6 7m W Patented June 2, 1931UNITED STATES PATENT OFFICE TORRENCE A. SWARTZ AND WILMER P. UHLER, OFTOTTENVILLE, NEW YORK, AS- SIGNORS TO THE S. S. WHITE DENTALMANUFACTURING COMPANY, OF PHILADEL- PHIA, PENNSYLVANIA, A CORPORATION OFPENNSYLVANIA VARIABLE RESISTANCE UNIT Application filed January 27,1925.

Our invention relates particularly to that class of resistance devicesin which the resistance elements are subjected to different degrees ofpressure to form a more or less intimate contact between said resistanceelements, whereby a consequent variation in the current passingtherethrough is attained; and is especially directed to such devices asmay be employed in connection with radio receiving and transmittingapparatus.

It is a well known fact that microphonic noises are caused in certaincircuits, such as the grid circuit of a radio receiving instrument orset, by the sliding contacts of the relatively movable elements of thecircuit varying mechanism, and that such noises detract materially fromthe pleasure of listening in.

The principal objects of our invention are to provide a resistance unitthat is so constructed andarranged as to avoid the use of slidingcontacts, whereby the undesirable microphonic noises incident to suchsliding contacts may be eliminated.

Other objects of our invention are to provide a resistance medium thatin itself will tend to refine the sound vibrations, and to further tendto dampen any microphonic sounds by providing yielding means connectingsaid resistance medium with means for varying the resistance of saidresistance medium,

Our invention further includes a variable resistance unit in which theresistance medium is disposed in separate piles formed of a plurality ofindividual blocks and arranged to be yieldingly compressed by balancedadjusting mechanism.

Specifically stated, the form of our invention as hereinafter described,comprises a casing of non-conducting material through the wall of which,electric terminal bindingposts extend, being connected through aplurality of blocks of especially prepared conductive resisting materialforming what is commonly termed a pile, and a connecting or'bridge barwhich may be yieldingly engaged therewith by springs adjustablymaintained under pressure by an adjusting screw, actuated by means of aknob, and bearing Serial No. 5,015.

Our invention also includes all of the various novel features ofconstruction and ar- L rangement as hereinafter more definitelyspecified.

In the accompanying drawings, Figure 1 is a sectional elevational viewof a resistance unit, conveniently embodying our invention; Fig. 2 is aperspective view-of one of the terminal binding-posts and its terminalplate, illustrated in Fig. 1; Fig. 3 is a perspective view of one of theblocks of resistance material, of which the resistance piles illustratedin Fig. 1 are composed; Fig. 4. is a perspective view of the connectingbar of electrical conducting material, which connects the resistancepiles shown in Fig. 1; Fig. 5 is a perspective view of one of the springseatplates illustrated in Fig. 1, which may preferably be composed ofinsulating material; Fig. 6 is a perspective view of the balancing leveror teeter bar arranged to equalize the pressure of the springs asillustrated in Fig. 1; and Fig. 7 is a sectional elevational viewsimilar to Fig. 1, showing a modified form of resistance unit embodyinga single pile.

In said figures, the preferred embodiment of the resistance unit isshown in Fig. 1 and comprises the casing 1 forming achamber 2 divided bythe transverse wall 3, and having the closure comprising the lid or cap5 conveniently secured to said casing, all of which is formed ofinsulating or non-conducting material.

The rear wall of thecasing 1 is provided with the apertures 6 and 7,through which the terminals 01 the binding-posts 9 and 10 extend so asto protrude exterior to the easing for the convenient connection of thewires 12 and 13 which are arranged to be secured by the set screws 15and 16, as shown in Fig. 1.

The inner ends of the binding-posts 9 and 10 are headed to provide theplates 17 and 18 respectively, which afford seats for the piles 19 and20 composed of the blocks 21 of resistance material. As shown, the pilesill iii

19 and 20 are disposed upon opposite sides of the transverse wall 3,which serves as a battle to prevent induction leaks, and said piles areconveniently connected by the electrical conducting bridge-bar 22,having the reduced connector 23, which serves to bridge and therebycomplete the circuit including the wires 12 and 13. The reducedconnector 23 which constitutes the central portion of the bridge bar 22operates to render this bridge bar flexible so that theend portions willmake and maintain intimate contact with the ends of the resistanceelements. 7

The resistance of the piles 19 and 20 may be conveniently varied byvariation in pressure tending to bring the blocks of resistance materialinto more or less intimate contact, and for this purpose springs 25 and26 are provided, preferably in co-axial relation with the respectivepiles 19 and 20.

The springs 25 and 26 may preferably bear upon the connecting-bar 22 andbe insulated therefrom by the spring seats 27 and 28, which maypreferably be of insulating material, and pressure applied thereto andvaried at will by the adjusting screw 29 whose head 30 bearscentrallyagainst the balancing lever or equalizing teeter beam or bar 32, the endportions of which engage the respective springs 25 and 26, so that anyaxial movement of the screw 29 efiected by rotation of its knob 33 tendsto vary the pressure equally upon both of said piles 19 and 20.

In the form of our invention as shown in Fig. 7, the resistance unitcomprises the easing 41 having the closure comprising the lid or cap l2enclosing the chamber 43 into which a portion of the rear wall isextended to provide a seat 15 for the contact plate 46 forming the headof the binding-post 47 extended through the aperture 48 in said rearwall, to protrude exterior to the casing, being pro vided with the setscrew 4.9 by which the lead wire 50 is engaged to said binding-post.

The contact plate 16 is electrically connected by the conducting bar 52with the pile 53 composed of a plurality of blocks 55 of resi,

' .tance material, seated upon the contact plate gas 56 forming the headof the binding-post 57 extended through the aperture 58 in the rear wallof the casing 41 to protrude exterior thereto, being provided with theset screw 59 by which the lead wire 60 is engaged to aid binding-post.

The resistance of the pile 53 may be conveniently varied by theadjusting'screw 62 which is in threaded engagement with the closure 42and which has the knob 63 by which I it may be rotated, and the head 65arranged to bear against the balancing or teeter bar 66, at its medialregion, to maintain the springs 67 and 68 on the insulated spring seats69 and 70, under varying degrees of compression and thereby vary theresistance of said pile 53, said springs 67 and 68 being co-axial withthe binding-posts 47 and 57, and equally spaced upon opposite sides ofthe axis of said adlusting screw 62. 7

Our invention is advantageous in'that the resistance maybe varied by therotation and consequent axial movement of the adjusting screw 29 whosehead 30 bears upon the equaliz'ing teeter bar 32 and rotates thereon ata point, to vary the degree of compression on the springs 25 and 26 andyieldingly vary the compression of the piles 19 and 20 and thereby varythe flow of current merely by such variation of pressure. varying theresistance, there are no wiping or scraping contacts, and as the causeof microphonic noises is eliminated, a consequent purity of toneresults. 7

7e are aware that there are on the market certain variable resistanceunits having two.

tion 21, are connected by the electricalconducting bridge plate 22having reduced connector 23. It can easily be seen by referring to Fig.1 or Fig. 7 that this connector bridge completes the electrical circuit,between the two'piles of composition blocks 21, and thereby all slidinor relatively movable parts of the unit are entirely outside of theelectric circuit, and are, in fact, insulated therefrom by insulatingpieces 27 and 28 in Fig. 1, or pieces 69 and 70 in Fig. 7 by ourconstruction and arrangement of the parts.

In other known types of compression units, slight movements of metal tometal contacts which are included in the electrical circuit arepossible, and have been found to cause microphonic noises, especially asthe higher resistance range of the unit is approached and when thedirection of rotation of the knob is reversed. These sliding contactsmay not necessarily be a part or function of such units, but may be aninherent def come by our construction and design.

We do not desire to limit our invention to the precise details ofconstruction and arrangement as herein set forth, as it is obvious thatvarious modifications may be made therein without departing from theessential features of our invention as defined in the appended claims. 7

Having thus described our'invention, we claim: 1. A variable resistanceunit free from all sliding contacts in the electrical circuit comprisinga casing, a plurality of pressure-re sponsive resistance elements, abridge bar in electrical contact with one end of each of said elements,an equalizing bar, springs interposed between said bars, and means tomove said equalizing bar to vary the compression of said springs.

By this method of ect which is over- 2. A variable resistance unit freefrom all sliding contacts in the electrical circuit, comprising acasing, two parallel resistance elements adapted to vary in resistanceaccording to the pressure thereon, a bridge bar in electrical contactwith adjacent ends of the elements so that said elements and bar areconnected electrically in series, an equalizing bar, springs interposedbetween the ends of said bars, and means to move said equalizing bar tovary the compression of said springs.

8. A variable resistance unit comprising a support, a pair of parallelresistance elements adapted to vary in resistance according to thepressure upon the ends thereof, a bridge bar electrically connected toadj aoent ends of the elements and adapted to exert mechanical pressurethereon, and means including two springs disposed coaxially with theresistance elements to exert pressure upon the bridge bar andtherethrough upon the resistance elements.

4. A variable resistance unit free from all sliding contacts in theelectrical circuit, comprising a casing, two parallel resistanceelements adapted to vary in resistance according to the pressurethereon, a bridge bar in mechanical and electrical contact with theother ends of the element-s so that said elements and bar are connectedelectrically in series, an equalizing bar parallel to said bridge bar,springs interposed between the ends of said bars whereby to exertpressure at the ends of said bridge bar, and an adjusting deviceoperating against said equalizing bar intermediate its ends, saidequalizing bar being capable of rocking movement with respect to saidadjusting device.

5. A variable resistance unit free from all sliding contacts comprisinga casing, a plurality of pressure-responsive resistance elements, abridge bar having its respective end portions in electrical contact withsaid resistance elements, and independent yielding means engaging theends of said bridge bar for moving the said ends toward said resistanceelements, said bridge bar having the central portion thereof cut away inorder to render said bar flexible whereby the end portions will makeintimate contact with the resistance elements.

In witness whereof, we have hereunto set our hands the 8th day of J an.,A. D., 1925.

TORRENCE A. SWARTZ. WILMAR P. UHLER.

